Conventionally, fuel economy of automobiles has been improved by reducing the rolling resistance of tires (i.e. by improving the rolling resistance property). Still, in these years, there is an increasingly growing demand for a reduction in fuel consumption of automobiles. With this demand has come a demand for a rubber composition with very low heat build-up which is used for producing a tread, which occupies a larger portion of a tire among various tire components.
For example, a method is known in which a tire is designed to have a double-layer tread part (i.e. a base tread and a cap tread), and a rubber composition with low heat build-up is used for the base tread. Still, there is a need for further reduction in heat build-up. Likewise, there is a demand for a rubber composition with lower heat build-up for use in tire components other than a tread, and sidewalls, which generate larger quantities of heat due to deformation, are also required to provide lower heat build-up.
Known as a method for producing a rubber composition with sufficiently low heat build-up is a method of reducing the amount of reinforcing filler in the rubber composition. In this case, however, the hardness of the rubber composition is decreased, and thereby tires produced therefrom are softer. Such tires may disadvantageously impair handling performance (handling stability) of automobiles and exhibit low wet grip performance and abrasion resistance. The strength of the rubber composition is also lowered and disadvantageously the tires will be easily damaged.
Patent Document 1 teaches that use of a modified styrene-butadiene rubber, which is modified with a predetermined organic silicon compound containing an alkoxy group, enables lower heat build-up, improved wet grip performance, and improved abrasion resistance. However, in order to achieve satisfactory levels of all of these performances, there remains a need for further studies. The breaking properties of the rubber composition should also be improved. The modified styrene-butadiene rubber used has only one modified end, and modification of both or two or more ends is not examined.    Patent Document 1: JP-A 2001-114938